'More than a hint' that dark energy isn't what astronomers thought

Don't confuse accelerated expansion with the cosmological constant. Accelerated expansion's origin is most likely the cosmological constant aka dark energy, but they are not the same thing. The cosmological constant itself arises naturally (kind of how an integration constant emerges for indefinite integrals) when you derive the field equations of general relativity. It is basically a geometric degree of freedom inherent to the Einstein-Hilbert action. Any astronomer who fit any model of the universe to some dataset in the past 25 years was fitting a constant. And even this new paper acknowledges that it will take some tremendous effort to convince people that this constant really is changing over time (which introduces a slew of theoretical issues that need to be explained). It will be particularly interesting to see how (if at all) this can be reconciled with measurements of things like the CMB, because stellar and galactic astrophysics is much less well understood.

Thank you for linking to this paper. It looks like a very comprehensive review of the "theory space", so to speak, that's currently being explored.

As a former astronomer, one thing to highlight here is that statistical uncertainties aren't usually all that important in assessing how likely a result in astronomy is to be true. The main issue you grapple with in the field are your systematic uncertainties. When you report your uncertainty, it always is an uncertainty in the context of some model. However, if certain assumptions that your models have made are wrong, you will have underestimated your true uncertainty. Unfortunately, systematic uncertainties can't be reduced just by getting more data --- you have to somehow verify that the different assumptions your model has made are correct.

Astronomers spend a lot of time arguing with each other about whether they have properly incorporated all their systematic uncertainties. For measurements of dark energy this very quickly gets you into the weeds of Type Ia supernova physics (which is made more difficult because we don't know for certain what Type Ia supernovae are), stellar physics in Cepheids, the effect of metallicity, selection bias effects, and on and on.

I think it's worth noting that the five sigma standard traditionally comes from particle physics, though. Cosmology doesn't have the luxury of being able to generate arbitrary amounts of data, and in fact has been a precise science for only sixty years or so. Hubble's first measurement of the expansion of the universe was off by a order of magnitude.

That's basically a particle physics threshold, because in particle physics you tend to do many, many experiments (usually you're doing thousands a second). It's hard to get something that certain in astronomy, where you've only got one universe to observe.

If you combine it with other data it's from 2.8 to 4.2 sigma. Pretty strong and it has gone up since last year with more data. Nothing definite yet, but certainly intriguing.

Agree that this is a much better summary, and generally gets to the point much better with relatively clear summaries of the issues. Once you get down to the mid-section, the NYT notably has a somewhat clearer description of the initial issues with supernovas and using them as references. The Dark Energy article [1] and the "Light Curve" portion of the Type Ia Supernova article [2] on Wikipedia offer further reading.

[1] https://en.wikipedia.org/wiki/Dark_energy

[2] https://en.wikipedia.org/wiki/Type_Ia_supernova#Light_curve

- Human's believe that Type Ia supernovas are the best way of measuring distance, because of an implied standard brightness and light curve that helps to avoid issues with only measuring redshift.

- Human's initially believed supernovas were supposed to show reduced brightness, further away, with a predictable reduction based on distance.

- Observations showed that supernovas were actually dimmer than expected.

- Implies that the universe is actually expanding, because supernovas were receding faster than expected.

- New results appear to show that the acceleration is decreasing. "there is something pushing galaxies away from each other, but it is not constant. It is declining.” "gently lifting its foot off the pedal"

I think this is also the better article. The other one is all over the place.

The Guardian is now paywalled. ... Hmmm not exactly - there's a page overlay which can be clicked past or something.

Yes, big rip was clearly disfavored by available data, and heat death ("big freeze") the most likely scenario. I haven't kept up in the past few years, abut AFAIK nothing so far has changed that.

All the images there have been prepared by the collaboration, not NYT. I know, since I've made one of those images.

And worst web developers it seems, I can't scroll the page.

> The laws of thermodynamics pretty much guarantees this anyways does it not?

Yes, but:

http://www.thelastquestion.net/

No, it could also end in a big crunch or big rip scenario. They'd have a finite lifetime of the universe.

Thermodynamics says there will be equilibrium, not that it will be all dark. But all the visible stars will run out at some point, and since nothing new can get into that sphere, each place in space will be "dark" at some point.

What about the CMBR, I've never heard anyone say that's decaying, but surely it's not an infinite source of energy?

Still, we’ve got a little while to go before star formation can no longer occur.

Some estimates put the star formation period from 1 to 100 trillion years.

I’d be more concerned about our collision course with the Andromeda Galaxy in four to five billion years.

The laws of thermodynamics are statistical laws, not fundamental laws. On a long enough timescale entropy might reverse

Sure, but this may be news to the target audience of the article.

They say the deadline was quite literally 6 days. Some of the employees rage-quit and started their own business (they are doing fantastic but work conditions are reportedly hellish). As far as we know, they were still tweaking the physical constants until not long ago.

[BUG #3451249]

Unlimited resource drain caused by conscious blobs of particles (a.k.a humans) invoking recursive thought patterns over their own existence.

Workaround: ponder function can return a feeling of existential dread accompanied by increased weights for headache "sensation", causing blob to terminate process.

Estimate: M

Label: Backend

This comment reminded me, with a smile, of Scott Alexander's Unsong: https://www.astralcodexten.com/p/unsong-available-in-paperba...

I once saw the Heisenberg Uncertainty Principle described as the result of the simulation creators using an 8 bit variable to store position and momentum combinations which were each themselves 8 bit values.

Call it professional bias, but I like to think about it as a big VM. If for some reason, things go awry, the (said) programmer will hit the pause button, then diligently go to the last valid snapshot, fix the bug and then get things going again. If this isn't desired, fixing the current mess is also an option.

The time required for fixing bugs isn't really an issue in this case, he can take as long as he likes.

So the first lead coder was this Lucifer guy. Wrote the whole code for the physical universe layer in like days on Red Bull and maybe speed.

Unfortunately he was shady and found to be embezzling from the company so he was fired. Only then did the team actually look at that code. Absolutely incomprehensible mess, and it looked like he left back doors in so he and his pals could manifest weird stuff in the universe and fuck with the inhabitants.

Like get this... a human draws a five pointed star on the ground and says some weird stuff and it trips some code that looks like obfuscated malware that calls out to a dodgy server, but we can't remove it because the whole thing is a giant spaghetti monolith.

The Lord put together a proper team of angelic hosts to rewrite the whole thing using solid software engineering practices, but of course that was aeons ago. But when it finally does ship we will get a new heaven and a new Earth with a whole list of promised features.

Archangel Michael, who is in charge of the project, keeps moving the deadline back, but he says they're making progress. It's a microservice architecture.

> a maximum speed

It's even hackier than that. Everything moves at c always, if not through space then through time or some combination.

I love this comment but I don't understand the "linked list" reference. What aspect of physics/the universe is that referring to? Also why does the maximum speed enable sharding? Struggling with that part too haha.